Hydrothermal synthesis of zinc stannate nanoparticles spectroscopic investigation

Transcription

1 DOI /s Hydrothermal synthesis of zinc stannate nanoparticles spectroscopic investigation Suresh Sagadevan 1 Jagpreet Singh 2 Kaushik Pal 3 Zaira Zaman Chowdhury 4 Md. Enamul Hoque 5 Received: 28 February 2017 / Accepted: 6 April 2017 Springer Science+Business Media New York 2017 Abstract This paper presents the study conducted on the synthesis and the investigations of Zinc stannate nanoparticles. Hydrothermal method was used for the synthesis. Characterizations for the products obtained were done with the help of powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV Vis absorption spectroscopy. The X-ray powder diffraction result was used to characterize the morphology and also it confirmed the well crystalline wurtzite structure. Typical electron microscopic investigations of SEM and TEM were used to study the morphology and the particle size. The formation of Zn 2 SnO 4 nanoparticles and their particle size were confirmed by the TEM analysis. The optical properties were analyzed using UV Vis absorption and PL spectrum. The FT-IR spectrum confirmed the presence of Zn 2 SnO 4 nanoparticles. The dielectric properties, e.g. dielectric constant, dielectric loss, and AC conductivity of the Zn 2 SnO 4 nanoparticles, were measured and studied as a function of frequency and temperature. Those nanoparticles exhibit quantum size effects of the optical * Suresh Sagadevan drsureshnano@gmail.com 1 Department of Physics, AMET University, Chennai , India 2 Department of Nanotechnology, Sri Guru Granth Sahib World University, Fatehgarh Sahib , India Wuhan University, 8 East Lake South Road, Wuhan , Wuchang, People s Republic of China Nanotechnology & Catalysis Research Centre, University of Malaya, Kula Lumpur, Malaysia Department of Biomedical Engineering, King Faisal University, Al Hofuf 31982, Al Ahsa, Kingdom of Saudi Arabia absorption spectrum. The influence of reaction conditions on the growth of Zn 2 SnO 4 nanoparticles demonstrates that high precursor concentration and high reaction temperature ( 200 C) is a favorable growth in the formation of zinc stannate. 1 Introduction Metal oxide semiconductors have multiple functions and promising application in optical and electrical fields due to which in recent years, they have gained much importance. Zn 2 SnO 4 with the band-gap of 3.6 ev is an important ternary metal oxide semiconductor and is a typical n-type semiconductor. On account of its high chemical sensitivity, magnificent, optical and electrical properties and low visible absorption, Zn 2 SnO 4 qualifies for a number of applications in gas sensors [1 3], solar cells [4, 5], photo catalysts [6 10], and negative materials for rechargeable lithium ion batteries [11, 12]. Due to these potential applications, an increasing interest of researchers is being evinced in the synthesis and study of Zn 2 SnO 4. Ternary oxide zinc stannate has exceptional optical and electrical properties offering much scope for research and drawing the attention of researchers [13]. Ternary oxide materials have been found to be of superior quality compared with binary oxides as they have the ability to tune the properties such as electrical conductivity, work function, and band gap energy by effecting changes in their composition [14, 15]. Hence, due to their typical physical and chemical properties the researchers show interest in them and make strenuous efforts towards the investigations of their technological applications; and also from the conventional bulk materials they vary notably. Usually, the nano sized particles have a high Vol.:( )

2 surface area with different surface defect properties and that is the reason the nanoscale particles exhibit a range of physical, chemical properties, better sinter capacity, larger catalytic activity and other unique properties. Therefore, by using diverse methods the technological value of Zn 2 SnO 4 has been exploited in several studies relating to the synthesis of this material. A few research outcomes by using various synthetic methods have been reported on the synthesis of zinc stannate. The present study focuses on the hydrothermal method employed for the synthesis and the characterization of Zn 2 SnO 4 nanoparticles and the outcomes are presented in this article. The characterization of as-prepared Zn 2 SnO 4 nanoparticles was determined by X-ray diffraction analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV analysis, FTIR and dielectric performances. Moreover, safe, low cost, high yield and controllable synthesis methods are always goals pursued in nanochemistry. 2.2 Materials characterizations and instrument details A powder X-ray diffractometer (Schimadzu model: XRD 6000 using CuKα) with a diffraction angle between 20 and 70 helped in the capturing of the XRD pattern of Zn 2 SnO 4 nanoparticles. By using Scherrer s formula the size of the grain was determined from the broadenings of the corresponding X-ray spectral peaks. On JEOL, JSM Scanning Electron Microscopy studies were carried out. With an accelerating voltage of 100 kv using an H-800 TEM (Hitachi, Japan) Transmission Electron Microscope image was taken. In the range of nm, using a Varian Cary 5E spectrophotometer UV Vis absorption spectrum for the samples was recorded. Using an FT-IR model Bruker IFS 66W Spectrometer the FT-IR spectrum of the Zn 2 SnO 4 nanoparticles was taken. Over the frequency range 50 Hz to 5 MHz using an HIOKI LCR HITESTER the dielectric properties of the Zn 2 SnO 4 nanoparticles were analyzed. 3 Results and discussion 2 Experimental details 2.1 Synthesis of Zn 2 SnO 4 nanoparticles All the reagents purchased from Merck were of analytical grade and used as received without further purification. The synthesis of Zn 2 SnO 4 using hydrothermal process required the precursors to be chosen; they were zinc chloride and tin chloride dihydrate with the mineralizer being NaOH. Tin chloride dihydrate (3 m mol) and Zinc chloride (3 m mol) were dissolved in 20 ml of double distilled water separately to form two transparent solutions. Then it was followed by the addition of 20 ml of NaOH (1 M) solution little by little into the tin chloride dihydrate transparent solution with the contents being stirred by a magnetic stirrer. Finally, these contents were added to zinc chloride solution drop-wise with stirring being maintained. The solution that was obtained last under room temperature was continuously stirred for 1 h until a white precipitate of the heterogeneous complex was obtained. The white hybrid complex, thus obtained was ultimately transferred into a 100 ml Teflon lined stainless autoclave with a fill factor of approximately 70%. The autoclave was sealed and placed in a furnace at 200 C for different time durations, so that the influence of the reaction time on the product structure and morphology could be studied. After cooling the autoclave to room temperature, the precipitate obtained was washed many times in double distilled water and in absolute ethanol by repeated centrifugution and ultrasonication. Thus, final products were obtained after purifying and dried in a laboratory oven at 80 C for 20 h. The X-ray diffraction patterns of the synthesized Zn 2 SnO 4 nanoparticles are shown in Fig. 1. In the standard data, the typical peak patterns shown in the figure can be indexed as the Zn 2 SnO 4 spinel cubic structure. The planes are (111), (220), (311), (222), (400), (511) and (440) of good crystalline Zn 2 SnO 4, respectively. All the diffraction peaks observed were in good agreement with the standard data of Zn 2 SnO 4 with spinel cubic structure. Confirming that the product obtained is phase pure, there was no characteristic peak detected for other impurities. The Scherrer formula was used to calculate the average nano-crystalline size (D): D = 0.9 β cos θ Fig. 1 Well crystalline XRD pattern of Zn 2 SnO 4 nanoparticles

3 Fig. 2 SEM images of Zn 2 SnO 4 nanoparticles Fig. 3 EDX spectrum of Zn 2 SnO 4 nanoparticles where λ denotes the X-ray wavelength, θ stands for the Bragg diffraction angle, and β means the FWHM of the XRD peak appearing at the diffraction angle θ. To calculate the average grain size for the most prominent peak at (311) Scherrer formula was used and it was found to be 22 nm. Figure 2 shows the SEM images of the Zn 2 SnO 4 nanoparticles, which revealed the formation of cubic shaped and some irregular shaped nanoparticles with their size being found to be 18 nm. From the SEM images, it was visible that the prepared Zn 2 SnO4 nanoparticles were evenly distributed. Figure 3 shows the EDX spectrum of the synthesized Zn 2 SnO 4 nanoparticles and reveals the elemental composition of the prepared. Further investigation was done by TEM analysis of morphology and structure of the Zn 2 SnO 4 synthesized nanoparticles. The samples resultant TEM image is shown in Fig. 4. From the image it is clear that the irregular agglomerated shape morphology of the samples changes to a well-defined flower like morphology and this helps us to understand that the SEM images are in good agreement with TEM images. The Transmission Electron Microscopic (TEM) analysis helped to measure the size of the particle formed and Fig. 4 TEM image of Zn 2 SnO 4 nanoparticles it was found to be ~38 nm. These observations show that the reaction temperature also significantly affects the morphology of the Zn 2 SnO 4 nanocrystals. It can be reasonably concluded that high precursor concentration and high reaction temperature ( 200 C) are favorable for the formation of Zn 2 SnO 4 nanoparticles. The optical absorption measurement corresponding to Zn 2 SnO 4 nanoparticles was also accomplished. For the as prepared Zn 2 SnO 4 nanoparticles the variation of the optical absorbance with the wavelength is shown in Fig. 5. In the range of nm wavelength the optical absorption coefficient was evaluated. As distinguished from bulk Zn 2 SnO 4 it can be observed that the absorption edge is slightly red-shifted, which leads towards nearing its absorption into the visible region. Hence, at higher wavelengths the samples are completely transparent. Later on a valence-to-conduction band transition occurs which causes an absorption peak at 340 nm exhibited by the UV spectrum which is in good agreement with the earlier reported

4 Fig. 5 UV Vis absorption spectrum of Zn 2 SnO 4 nanoparticles Fig. 7 PL spectrum of Zn 2 SnO 4 nanoparticles Fig. 6 Optical band gap energy of Zn 2 SnO 4 nanoparticles results. Around 380 nm a strong light absorption rise was seen which could be assigned to intrinsic band gap absorption [16]. It is clearly observed that the Zn 2 SnO 4 nanoparticles have a steep absorption edge, which indicates the absorption relevant to the band gap is due to the intrinsic transition of the semiconductors and not because of the transition from impurity levels [17, 18]. The plots of the (αhν) 2 against photon energy (hυ) are depicted in the Fig. 6 and the value of band gap was found to be 3.84 ev. In order to confirm the above statement, in room temperature Photo Luminescence (PL) spectrum of as-prepared Zn 2 SnO 4 nanoparticles was taken at the excitation level of 250 nm and is shown in Fig. 7. From the spectrum a broad green emission peak is observed at 502 nm. It is known that Fig. 8 FTIR spectrum of Zn 2 SnO 4 nanoparticles band gap of bulk Zn 2 SnO 4 is 3.6 ev, so emission peak at 502 nm is not due to the bandto-band gap emission. So, in the present study the strong green peak may arise due to the effect of oxygen vacancies. Figure 8 shows the FTIR spectrum recorded in the range cm 1 for zinc stannate nanoparticles. Due to the symmetric stretching vibration of ZnO and SnO 2 groups a broad absorption peak was noted at cm 1 and in Zn 2 SnO 4 this band could be assigned to the Sn O Zn bonding. The presence of hydrogen bonds was indicated by the absorption peaks at 1600 and 3278 cm 1. The C H

5 vibration mode could be attributed to the organic residuals and was assigned by the absorption peak at 1426 cm 1. In ZnO the possible bonding of Zn was assigned by the peak at 2241 cm 1 and in Zn 2 SnO 4 the Sn O stretching vibrations were attributed to the peak at 1170 cm 1. These results are in good agreement with the earlier reported results [19]. Moreover, the chemical composition of Zn 2 SnO 4 nanoparticles was studied by means of Raman spectrum. The nanocrystalline zinc stannate causes an additional peak at 626 cm 1 as shown in Fig. 9. The positions of all other Raman peaks in the spectrum of the nanostannate are the same as those observed for the bulk spinel. Moreover, the spectrum of the nanomaterial displays a marked difference in relative intensity and width of the vibrational peaks when compared with those of bulk Zn 2 SnO 4. To interpret these spectral features, and especially, the appearance of the additional Raman phonon mode at 626 cm 1, it should be emphasized that the cation redistribution between the (A) and (B) lattice sites of a spinel crystal may alter its symmetry and manifests itself by a larger number of active vibrational modes in the Raman spectrum [20, 21]. The dielectric studies were done at different temperatures for the pellets of Zn 2 SnO 4 nanoparticles in disk form. The temperature and the frequency variations of the dielectric constant of Zn 2 SnO 4 nanoparticles as depicted in Fig. 10. The dielectric constant has high values at the lower frequency region and with the increase in frequency it decreases. Due to the existence of all the four polarizations, namely the space charge, orientation, ionic, and electronic polarizations the value of the dielectric constant at low frequencies is very high and due to the loss of these significant polarizations, its value at higher frequencies is low [22]. It is also noticed from the plot that near the grain boundary interfaces the presence of space charge polarization is Fig. 10 Dielectric constant with frequency variation plot for Zn 2 SnO 4 nanoparticles ascribed by the dielectric constant which increases with an increase in the temperature and leads to the purity and exactness of representation of the sample [23]. The temperature and the frequency deviations of the dielectric loss of Zn 2 SnO 4 nanoparticles are shown in Fig. 11. It can be observed that at all temperatures with higher frequencies the loss angle has almost the same value and to increase in the frequency the dielectric loss decreases. The orientation of the molecules in the direction of the used electric field in polar dielectrics needs a part of the electric energy to saturate the forces of internal friction [24]. For the rotations of dipolar molecules and other kinds of molecular displacement from one position to another, has been utilized Fig. 9 Raman spectrum of the zinc stannate (Zn 2 SnO 4 ) nanoparticle crystalline peak Fig. 11 Dielectric loss with frequency variation plot for Zn 2 SnO 4 nanoparticles

6 one more part of the electric energy, which involves energy losses. A dielectric loss is caused by an absorption current which is created by the space charge formation occurring in the inter phase layers; this explains the context that in nano phase materials, inhomogeneities similar to defects exist [25]. For the AC conductivity the frequency reliance behavior is shown in Fig. 12 in the temperature interval C. With the increase in the frequency the AC conductivity increased for all temperatures. It was observed that with the increase in the frequency of the applied AC field, the AC conductivity gradually increased due to the electron hopping frequency [26]. The higher frequency reduction in space charge polarization could cause an increase in conductivity. 4 Conclusion We have developed a simple and reproducible hydrothermal methodology for the preparation of Zn 2 SnO 4 nanoparticles. However, this hydrothermal technique involved the use of sacrificial templates or guiding catalysts, whose removal may complicate the application of the nanostructures, and the yields are relatively low. The formation of the nanoparticle is dependent on the high temperature and high precursor concentration conditions. The method is facile and suitable for the large scale preparation of highquality Zn 2 SnO 4 nanoparticles. The X-ray diffraction pattern has revealed the well crystalline peak that resulted for Zn 2 SnO 4 nanoparticles. The nanoscale size and morphology of the desired samples have been confirmed by using SEM and TEM. By using TEM the size of the Zn 2 SnO 4 nanoparticles has been distinguished, which also has led Fig. 12 AC conductivity with frequency plot for Zn 2 SnO 4 nanoparticles to the determination of the size of the prepared Zn 2 SnO 4 nanoparticles. The elementary peak detection of Zn 2 SnO 4 nanoparticles has been done by EDX spectroscopy. Hence, with the support of UV Vis absorption spectrum the optical properties have been investigated. The optical energy band gap value has been calculated to be 3.84 ev. The formation of Zn 2 SnO 4 nanoparticles has also been supported by FT-IR and FT-Raman spectrum. Detailed investigations of electrical responses, e.g. dielectric constant, dielectric loss, and AC conductivity has been performed by considering variations with frequency and temperature for Zn 2 SnO 4 nanoparticles. With an increase in the frequency both the dielectric constant and the dielectric loss have decreased. With an increase of the temperature and the frequency, AC electrical conductivity has been found to increase. Moreover, synthesized Zn 2 SnO 4 nanoparticles can form stable colloidal dispersions and, therefore, are good for solution processing and device integration. References 1. Y.-Q. Jiang, X.-X. Chen, R. Sun, Z. Xiong, L.-S. Zheng, Mater. Chem. Phys. 129, (2011) 2. Z. Chen, M.H. Cao, C.W. Hu, J. Phys. Chem. C 115, (2011) 3. Y.Q. Jiang, C.X. He, R. Sun, Z.X. Xie, L.S. Zheng, Mater. Chem. Phys. 136, (2012) 4. B. Tan, E. Toman, Y.G. Li, Y.Y. Wu, J. Am. Chem. Soc. 129, (2007) 5. J.J. Chen, L.Y. Lu, W.Y. Wang, J. Phys. Chem. C 116, (2012) 6. J. Zeng, M.D. Xin, K.W. Li, H. Wang, H. Yan, W.J. Zhang, J. Phys. Chem. C 112, (2008) 7. M.A. Alpuche-Aviles, Y. Wu, J. Am. Chem. Soc. 131, (2009) 8. Z. Ai, S. Lee, Y. Huang, W. Ho, L. Zhang, J. Hazard. Mat. 179, (2010) 9. Z. Tian, C. Liang, J. Liu, H. Zhang, L. Zhang, J. Mater. Chem. 22, (2012) 10. T.K. Jia, J.W. Zhao, F. Fu, Int. J. Photoenergy 2012, 6 Article ID (2012) 11. N. Feng, S.L. Peng, X.L. Sun, Mater. Lett. 76, (2012) 12. A. Rong, X.P. Gao, G.R. Li, J. Phys. Chem. B 110, (2006) 13. P. Jayabal, V. Sasirekha, J. Mayandi, V. Ramakrishnan, Superlattices Microstruct. 75, (2014) 14. C. Chen, G. Li, J. Li, Y. Liu, One-step synthesis of 3D flowerlike Zn 2 SnO 4 hierarchical nanostructures and their gas sensing properties. Ceram. Int. 41, (2015) 15. Z. Li, Y. Zhou, H. Yang, R. Huang, Z. Zou, Electrochim. Acta 152, (2015) 16. L. Shi, Y. Dai, J. Mater. Chem. A 1, (2013) 17. M. Najam Khan, M. Al-Hinai, A. Al-Hinai, J. Dutta, Ceram. Int. 40, 8743 (2014) 18. J. Tauc, R. Grigorovici, A. Vancu, Phys. Stat. Sol. 15, 627 (1966) 19. J. Emima Jeronsiaa, L. Allwin Joseph, M. Mary Jaculine, P. Annie Vinosha, S. Jerome Das, J. Taibah Univ. Sci. 10, (2016) 20. M. Lazzeri, P. Thibaudeau, Phys. Rev. B 74, (2006)

7 21. P. Chandramohan, M.P. Srinivasan, S. Velmurugan, S.V. Narasimhan, J. Solid State Chem. 184, 89 (2011) 22. S. Suresh, C. Arunseshan, Appl. Nanosci. 4, (2014) 23. S. Suresh, Appl. Nanosci. 4, (2014) 24. S. Suresh, J. Podder, I. Das, J. Mater. Sci. 27, (2016) 25. K. Tamizh Selvi, K. Alamelumangai, M. Priya, P.M. Rathnakumari, S. Kumar, S. Suresh, J. Mater. Sci. 27, (2016) 26. S. Suresh, J. Podder, Mater. Res. 19, (2016)